A power converter is a power processing circuit that converts an input voltage waveform into a specified output voltage waveform. In many applications requiring a DC output, switched-mode DC/DC converters are frequently employed to advantage. DC/DC converters generally include an inverter, an input/output isolation transformer and a rectifier on a secondary side of the isolation transformer. The inverter generally includes a switching device, such as a field effect transistor ("FET"), that converts the DC input voltage to an AC voltage. The input/output isolation transformer, then, transforms the AC voltage to another value and the rectifier generates the desired DC voltage at the output of the power converter.
Conventionally, the rectifier comprises a plurality of rectifying diodes that conduct the load current only when forward-biased in response to the input waveform to the rectifier. Alternatively, a more efficient rectifier can be attained in converters by replacing the rectifying diodes with active switches, such as FETs. The switches are periodically toggled between conduction and nonconduction modes in synchronization with the periodic waveform to be rectified. A rectifier employing active switches is conventionally referred to as a synchronous rectifier.
When the input voltage is, for instance, stepped down across a step-down isolation transformer in the power converter, the current capacity required on the secondary side of the transformer and the rectifier is significantly higher than that on the primary side of the transformer. As a result, the power converter suffers efficiency losses on the secondary side of the isolation transformer that impair the overall performance of the power converter. The path between the isolation transformer and the rectifier is of acute interest because it carries high AC that is subject to onerous losses. Furthermore, the path between the inverter and the isolation transformer and, especially, the path between the isolation transformer and the rectifier realize stray inductances that also impair the efficiency of the power converter. Therefore, efforts to minimize the losses associated with the paths between the inverter or switch, isolation transformer and the rectifier would improve the overall performance of the power converter.
In addition to efficiency improvements, increased power density is a continuing goal of modern power supply (e.g., power converter) design. High power density is particularly crucial in applications wherein the allocated space for the power supply relative to the power output is restricted. In addition to being highly compact, the power supply should be efficient to limit heat-creating power dissipation. To dissipate the heat generated in the power supply, typically, heat sinks are mounted on the power supply components. Individual heat sinks for the discrete components of the power converter raise some concerns, namely, it creates additional costs that cannot be readily absorbed in a cost competitive market; also, it decreases the flexibility necessary to design a higher circuit density power supply.
As those of ordinary skill in the art understand, it is, therefore, highly desirable to provide a protective, heat-dissipating package for the electronic circuitry of the power supply. Often, such circuitry can be encapsulated or "molded," wherein an encapsulant is formed about the circuitry to yield a unitary, board-mountable package. One well known configuration for board-mountable package is a so-called dual in-line package ("DIP"), wherein electrical leads protrude from opposing sidewalls of the package. The leads are advantageously so arranged to allow the package to be mounted to a circuit board by various conventional soldering processes. DIPs are widely used for packaging integrated circuits, most often in computer-related environments.
The advantage of packaging discrete power components into an integrated power module has been addressed in the prior art. More specifically, a surface-mounted transformer-diode power module is disclosed in a U.S. patent application, Ser. No. 08/385,495, filed on Feb. 8, 1995, by Lotfi, et al., entitled "High Frequency Surface Mount Transformer-Diode Power Module," commonly assigned with the present invention and incorporated herein by reference. Lotfi, et al. discloses a transformer-diode module that packages a transformer and diode into a single module to take advantage of higher power density and improved electrical performance by coupling the two discrete components together. However, Lofti, et al. may be improved upon to further increase the power density and electrical performance of a power supply device incorporating multiple power components.
Accordingly, what is needed in the art is an integrated power module, including an inverter or switch, transformer and rectifier, in an encapsulated, integrated package that may be implemented in a high power density and high performance power supply.